Fibrous elements have long been used by the automotive industry to form moldable fiber products. These products may utilize knitted fabrics, woven fabrics, and nonwoven fabrics. Exemplary nonwoven fabrics may be needle punched, spun bonded, spun laced, thermally bonded, or chemically bonded.
Most thermally bonded nonwoven fabrics are made by intimately blending a high melt temperature fiber with a low melt temperature fiber. This allows the low melt temperature fiber to be melted during a heating process, such as thermoforming, to form a stiff, molded portion of the fabric. Thermoforming may be used, for example, to conform the molded portion to a surface of an automobile. Not all fibrous elements perform equally when heated. For example, most low melt temperature fibers have a glass transition temperature (“Tg”) of less than 90° C.; many high melt temperature fibers are similarly limited. As a result, many nonwoven fabrics are limited to a maximum heat deformation temperature of 90° C.
While a deformation temperature of 90° C. or less is adequate for many interior applications, the advent of using fibrous products in exterior areas as well as near engine components has driven the need for higher heat deformation temperatures. For example, many automotive manufacturers are now demanding nonwoven fabrics with a heat deformation temperature of at least 120° C. Demands for nonwoven fabrics having a heat deformation temperature of 150° C. are also common.
A deformation temperature of 120° C. can be achieved by using Polypropylene (“PP”) as the low melt temperature fiber. But PP starts to soften at 140° C. and fully melts at 165° C. Thus, PP cannot be used to meet a deformation temperature of 150° C. Polyester or Nylon may be used as high melt temperature fiber; however, they do not recyclable back into itself. Thus, neither the molding scrap nor the finished products are recyclable back into themselves for new production. Both of these challenges limit the usefulness of PP or Polyesters within moldable fabrics.
Excessive deformation is another concern. For example, deformation may be detrimental to vehicle safety if the molded portion is exposed to the exterior of the vehicle. Deformation of a molded exterior portion is also detrimental to the appearance of the vehicle and can create stress on the fastening systems. Thus, deformation resistance is also a performance requirement of any moldable fabric.
Bi-component fibers have also been used to make moldable fiber products. Typically, these fibers have a core-sheath configuration, wherein an exterior sheath formed from the low temperature melt fiber is coaxial with an interior core formed from the high temperature melt fiber. Some bi-component fibers may be adapted to have a heat deformation temperature greater than 150° C. For example, some bi-component fibers employ crystalline polymers that melt at 160-185° C. Yet even these “high temperature” fibers may not be ideal for use in a moldable fabric because, once melted, they revert to an amorphous structure with a Tg of 70-90° C. As a result, any moldable fabric made with existing bi-component fibers may suffer from excess deformation if exposed to temperatures greater than 90° C. Moreover, while most bi-component fibers can be recyclable, the recycling process may be greatly complicated by the bond between the exterior sheath and the interior core.
In addition to the performance requirements stated above, many moldable fiber products must also meet strict performance requirements for airflow, flexibility, flame resistance, smoke resistance, and durability. For example, some products must achieve a significant reduction in airflow (or increase in “Rayls,” the measurement of airflow resistance) and have a flexural modulus optimized for strength and durability.
These additional requirements can be difficult to meet because many known fiber elements are porous. As a result, many existing products may distort and fail by absorbing (or adsorbing) water, oil, and other engine fluids.
This problem is related to flame and smoke resistance. For example, a product that is more likely to absorb oil is also less likely to be flame and smoke resistant; instead, such products are more likely to generate large amounts of smoke as the oil burns off during a fire.
Generally, most fibrous products will absorb or adsorb water, oil, and other engine fluids, which increase the weight which causes them to distort and fail. Further, there is a need to improve flame resistance to a much higher standard than the MVSS-302 test. There is also a need to reduce smoke generated for the safety of vehicle occupants in case of a fire.
A need exists for a product that does not exhibit failure during heat aging up to 150° C.; has resistance to water, oil, and engine fluids, has low flame spread and low smoke, and is recyclable back into itself. Further, these moldable products must have excellent abrasion resistance against sand & gravel.
Therefore, need exists for a moldable fabric adapted to meet the performance characteristics noted above. Further improvements are required.